What is the most common cause of a mass found in a child with macrocephaly, macroglossia, and hypospadias?

In a child presenting with macrocephaly, macroglossia, and hypospadias, the associated conditions suggest a possible genetic syndrome such as overgrowth syndromes, particularly Beckwith-Wiedemann syndrome. Wilms' tumor, which is a common renal tumor in children, has been associated with Beckwith-Wiedemann syndrome. The triad of macrocephaly, macroglossia, and hypospadias points towards this syndrome, where the risk of developing Wilms' tumor is increased.

This relationship is crucial because the manifestations of the syndrome can direct clinicians to monitor for Wilms' tumor and other neoplasms. Although other tumors like neuroblastoma, hepatoblastoma, and retinoblastoma can occur in childhood, they are not primarily associated with the specific combination of symptoms presented in this scenario. Therefore, Wilms' tumor stands out as the most relevant concern for a mass in the context of these findings.